CK7 (KRT7) is an intermediate filament type II keratin that is expressed in a number of simple epithelia including breast, lung, bladder, female genital tract (ovary, endometrium and fallopian tube), gastrointestinal tract, gallbladder, hepatic ducts, pancreatic ducts, and urinary tract. CK7 is usually positive in breast cancers as well as ovarian, lung, thyroid, endometrial, bladder and chromophobe renal cell carcinomas. It is negative in colon cancer, hepatocellular carcinomas, squamous cancers, and prostate adenocarcinomas. Staining for this target is expected to be cytoplasmic. References: Front Oncol. 2018 Dec 18;8:634, PMID: 30619768; Manual of Diagnostic Cytology (2 ed.). 2003. Greenwich Medical Media, Ltd. p. 173. ISBN 978-1-84110-100-2; The Journal of Cell Biology. 2006. 174 (2): 169–74, PMID: 16831889.